The present application relates generally to an improved data processing apparatus and method and more specifically to an apparatus and method for dynamically adjusting an operating state if a data processing system is running under a power cap.
Power capping is a technique for controlling a rate of energy consumed in a group of computing systems, a single computing system, or a subsystem within a computing system over a period of time. The value or setting for a power cap is generally defined by an external or internal management entity. Within a computing system, a power control loop measures power at the input to the computing system and adjusts the input power level of components in the computing system, such as through adjusting voltage, frequency, or the like, to meet the identified power cap setting. If the measured power is less than the power cap, there is more power available for the components of the computing system. Thus, the available power level may be raised by increasing the performance and power consumption of the components of the computing system. If the measured power level exceeds the power cap, the power level must be reduced which reduces the performance of components in the computing system.
Current power cap solutions select conservative voltage/frequency settings based on a recent power control loop interval to provide an adequate power consumption margin in case a workload of the computing system increases before the next power control loop adjustment interval. The power control loop determines a “safety margin” that is a function of control loop frequency and maximum change in workload activity. The power control loop measures power at the current voltage and frequency setting. If the measured power is within the safety margin, the power control loop reduces voltage and frequency of the components in the computing system. If the measured power is lower than the safety margin, the power control loop increases the frequency and voltage of the components in the computing system. However, the conservative safety margins may also waste a power budget and limit the ability to aggressively manage power.